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Manipulating Relational Databases
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Select
SELECT FirstName, LastName
FROM Employees
WHERE City = "Reading"
Retrieval of Data
Select
CREATE USER 'daniel'@'localhost'
IDENTIFIED BY 'my_password';
We also use SQL to search for and retrieve specific data from the database.
We use this so we can then produce reports and perform other functions based on the data.
The Select command is used for this.
Administration of Users
Select
RBMSs are often designed to be accessed by many different users.
We use SQL to assign usernames, passwords & priviliges.
The two main commands for this are:
- Create User - add a user to the current database.
- Grant - assign access privileges to an existing user.
GRANT ALL ON *.*
TO daniel'@'localhost';
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Update
UPDATE Employees
SET LastName = 'Thompson', City= 'Swindon'
WHERE EmpID = 1
Security, Integrity & Recovery
Update, Insert & Delete
The granting of privileges is important for security as it limits damage that can be caused by an individual user.
There are also SQL commands that are designed to ensure data integrity is maintained & to backup data.
These can be quite different between different RDBMSs though.
Insert
When you want to modify the data being stored in your database you will use:
- Update - change the data stored in the fields of an existing record.
- Insert - add a new record into a table of your database.
- Delete - delete an existing record from your database.
INSERT INTO Employees (FirstName, LastName, Address, City, PostCode)
VALUES ('Michael', 'Cross', '21 Bodmin Road', 'Reading', 'RG4 6XZ');
Delete
DELETE FROM Employees
WHERE EmpID = 1;